夜间灯光数据支持下西藏人类活动强度变化对生态系统调节服务的影响

西藏自治区特殊的高寒生态系统对人类活动具有高度敏感性,定量评估系列政策实施下西藏生态系统调节服务对人类活动强度变化的响应有助于西藏生态政策和空间规划的调整完善。本研究基于西藏1980年和2015年土地利用现状数据及1992—2013年DMSP/OLS夜间灯光指数数据,借助GIS空间分析功能分析了居民点用地和夜间灯光强度的变化;并结合生态系统调节服务空间数据,利用相关分析对居民点用地和夜间灯光变化所反映的人类活动强度变化对西藏生态系统水土保持和防风固沙服务的影响进行研究。结果表明：① 1980—2015年,西藏新增居民点用地212.06 km²,减少居民点用地44.99 km²,其中,新增居民点用地中62%为城镇用地,减少的居民点用地中95.88%为农村居民点;居民点用地变化主要发生在藏南河谷区;② 自治区内居民点用地扩张一定程度上直接导致夜间灯光强度增加,“一江两河”流域土地整治工程和农牧民安居工程等促进了当地人类活动强度增加,区内部分乡镇因进城务工和易地扶贫搬迁造成了当地人类活动强度的下降;③ 西藏2015年防风固沙服务较1990年有整体增强趋势,水土保持服务除藏东高山峡谷区外均有大幅度退化趋势;④ 对居民点用地进行的还林、还草整治工程等人类活动有利于促进生态系统防风固沙服务的恢复;人类活动强度的增加极易导致水土保持服务的退化,“一江两河”流域体现最为明显。研究能为西藏国土空间规划和生态政策的制定和调整提供参考。

Changes in Human Activity Intensity and Influence on Ecosystem Regulating Services: A Study of Tibet based on Night Light Data

The alpine ecosystem of the Tibet autonomous region is extremely fragile and highly sensitive to climate change and human activities. In recent years, the government implemented several conservation policies, aiming to simultaneously conserve the degraded ecosystem and guarantee the livelihood of local residents. These policies include grassland ecological compensation policy, settlement of nomads, and relocation of poor people from inhospitable areas. Human activity intensity varied temporally and spatially during the implementation of those polices, which can be reflected by land use transition and population migration. Therefore, quantitative assessment of the response of grassland ecosystem services to land use and human activity changes can help with the adjustment and improvement of Tibet's ecological policies and spatial planning. We used GIS spatial analysis to analyze the changes of residential land and night light intensity of Tibet, based on the land use maps of 1980 and 2015 and DMSP/OLS night light index data from 1992 to 2013. The influence of changes in human activity intensity (i.e., as reflected by the change of residential land and night light) on soil and water conservation and sand-fixing services in the ecosystem of Tibet was studied by correlation analysis. Results show that:(1) From 1980 to 2015, the newly constructed residential land in Tibet was 212.06 km², of which 62% was urban. Residential areas shrunk by 44.99 km², of which 95.88% were rural. The changes of residential land mainly occurred in the south Tibetan valley. (2) The expansion of land use in residential areas directly led to the increase of light intensity at night to a certain extent. Land consolidation projects in the Yarlung Zangbo River and its two tributary basins and the project of peasant and herdsman's safe housing promoted the intensity of local human activities, while some townships in the region reduced the intensity of local human activities due to migration and poverty alleviation. (3) The sand-fixing service in Tibet increased from 1990 to 2015, and the soil and water conservation service showed a notable degradation trend except for the high mountains and valleys in eastern Tibet. (4) There was a positive correlation between sand-fixing service and the reduced amount of land in residential areas, while there was a negative correlation between soil and water conservation service and the increased amount of land in residential areas, the reduced amount of trees in residential areas, and the trend value of night light index. Human activities such as reforestation and grassland restoration contributed to the sand-fixing services, and the increase of human activity intensity could easily cause degradation of soil and water conservation services, especially in the Yarlung Zangbo River and its two tributary basin areas. Our findings could help improve Tibet's spatial planning and ecological policies.